October 13, 2025 • 20 mins
Covers a vast range of topics fundamental to the specialty, including the biological basis of craniofacial development from prenatal stages to postnatal growth, focusing heavily on bone remodeling, genetic influences, and the formation of the dentition. Significant attention is paid to the classification, examination, and diagnosis of malocclusion, utilizing various methods like Angle's classification and cephalometric analysis (including Steiner's and McNamara's analyses). Furthermore, the text details the mechanics and application of orthodontic treatment, covering removable and fixed appliances, root resorption risks, and the management of complex issues such as impacted teeth, hypodontia, and craniofacial syndromes like cleft lip and palate, alongside the crucial topic of long-term retention and relapse.
Mark as Played
Transcript
Episode Transcript
Available transcripts are automatically generated. Complete accuracy is not guaranteed.
Speaker 1 (00:00):
Welcome back to the deep dive. Today. We're really getting
into some foundational knowledge for anyone heading into dentistry, especially orthodonics.
That's right. Our source is a classic, The Handbook of
Orthogotics by Dibious from two thousand and nine.
Speaker 2 (00:14):
A cornerstone text.
Speaker 1 (00:15):
Yeah, and if you're a student or maybe just starting out,
you know these early chapters are packed angles, classifications, growth theories.
It's a lot, it is.
Speaker 2 (00:26):
So our goal today is to kind of cut through that,
synthesize the really key concepts classification, development, diagnosis, the basic
principles you need exactly.
Speaker 1 (00:37):
We want to give you a complete, detailed summary, but
you know, make it stick, provide those core scientific nuggets
you need for clinical practice.
Speaker 2 (00:43):
And we have to start some more fundamental like what
even is normal occlusion?
Speaker 1 (00:47):
Good starting point, so when we talk aclusion, there's static
and functional. Right. Historically, where did the idea of ideal
static occlusion come from?
Speaker 2 (00:56):
Well you have to start with Edward Engel. His whole
focus really was on the first permanent.
Speaker 1 (01:00):
Molars, just the molars pretty much.
Speaker 2 (01:03):
He defined normal occlusion based on one thing, the mesiobuckle
cusp of the upper first molar, fitting neatly into the
sulcus between the buckle cusps of the lower first molar.
That was his key to the whole system.
Speaker 1 (01:15):
Okay, but we know now that just having the molars
line up isn't the whole picture for a great smile
or a stable bike. H What did Laurence Andrews ad
later with his six keys?
Speaker 2 (01:26):
Right, Andrews really fleshed it out. He gave us a
much more detailed blueprint for what an ideal finish looks like.
His six keys covered the molar relationship, sure, like angles,
but also things like specific crown angulation the tip you know,
messiodistally and crown inclination which is the torque labiolingually plus
no rotations, tight contacts, the works.
Speaker 1 (01:47):
And these keys are still fundamental today for treatment goals
right for aesthetics.
Speaker 2 (01:50):
And still absolutely they define what we're aiming for.
Speaker 1 (01:53):
Okay, so that's static. What about when the jaw is
actually moving functional occlusion? What needs to happen then too?
Speaker 2 (01:59):
Like protective teeth, functionally it's about guidance and contacts. You
need what's called anterior protection. So when you move your
jaw side to side, ideally, only the canines should be
touching and guiding the movement. That's canine guidance or sometimes
group function or sometimes yeah, a few posterior teeth might
share the load, that's group function. But the main goal
(02:20):
is immediate separation disclusion of all the other back teeth.
Same idea, when you move forward protrusion, only the incisors
should guide incisile guidance.
Speaker 1 (02:29):
And why is that separation that disclusion so important?
Speaker 2 (02:32):
It minimizes harmful sideways or sheer forces on the molars
and premolars. They are designed for that. So that's the
first thing. Second is posterior protection, meaning meaning when you
bite down fully in your maximum bite what we call
ICP intercustible position, you need solid simultaneous contacts on both
sides in the back, multiple posterior teeth hitting evenly.
Speaker 1 (02:54):
Okay, And what about the front teeth in that.
Speaker 2 (02:56):
Position, Critically, the front teeth the incisors should ideally be
just slightly out of contact and ICP no heavy anterior
contact stopping you from fully closing in the back.
Speaker 1 (03:06):
Makes sense? And the third piece you often hear COO
and CR mentioned ICP and RCP. Now I guess right.
Speaker 2 (03:13):
The third point is a relationship between that maximum byte ICP,
which used to be called centric occlusion or CO, and
the jaw's most retruded hinge position RCP or retruded contact position,
sometimes called cr and Ideally, ideally these two positions should
be very close together, maybe just a tiny bit of
freedom to slide forward from RCP into ICP. If there's
(03:35):
a big difference, a big slide, it often points to
an interference or instability.
Speaker 1 (03:39):
Okay, so that defines our baseline normal. Now let's talk
about when thing's deviate malaclusion. If the molars aren't class one,
we use angles system.
Speaker 2 (03:47):
Right yeap Angle's classification is still the workhorse. Class one
is that ideal molar relationship we talked about. Class two
means the lower molar is distal, or further back than
it should.
Speaker 1 (03:56):
Be, and that's split into division one and two. Correct.
Speaker 2 (03:59):
Division one is class two molars with flared out protruding
upper incisors. Division two is class two molars but with
the upper incisors tipped.
Speaker 1 (04:07):
Back retroclined, and class three.
Speaker 2 (04:09):
Class three is the opposite. The lower molar is mesial
or further forward than normal. And remember clinically, it's rarely
a perfect full cusp difference. We often describe these relationships
more precisely, like half unit class two or third unit
class three.
Speaker 1 (04:26):
Got it, And then there's a parallel system just for
the incisors the British standards one exactly.
Speaker 2 (04:31):
The incisor classification looks purely at the front teeth, specifically
where the lower incisor edge sits relative to the singularm plateau,
that little bump on the back of the upper incisors.
Speaker 1 (04:41):
The class one is normal.
Speaker 2 (04:42):
Class one is normal, the lower incisor hits the singular area.
Class two it's behind the singulum again. Div one if
the upper incisors are proclined, If two if they're.
Speaker 1 (04:50):
Retroclined, and class three incisors.
Speaker 2 (04:52):
That's when the lower incisor edge is in front of
the upper singulum plateau. So you have a reduced or
even reverse overjet and underbyte essentially.
Speaker 1 (05:00):
Okay, that covers classification. Let's shift gears to why maleeclusions
happen Etiology, the classic nature versus nurture debate. What does
the source say about strong genetic links?
Speaker 2 (05:11):
Oh, genetics is definitely a major player for some things.
The source highlights skeletal patterns, especially mendibular prognathism. You know
of strong lower jaw class three that shows really high
heritbility runs in families.
Speaker 1 (05:24):
Any other examples.
Speaker 2 (05:26):
Yes, Specific dental anomalies too, like pallatally impacted canines, those
upper canines stuck in the roof of the mouth. They're
often linked genetically with missing or small lateral incisors in
the same family. It's a pattern, but it's.
Speaker 1 (05:38):
Not all genes. Right. The environment must play a role.
Where does that come in?
Speaker 2 (05:42):
Absolutely, the environment, often acting through the soft tissue envelope,
is huge. Think about habits. A persistent thumb or finger
sucking habit that can push the upper incisors forward, create an.
Speaker 1 (05:55):
Open bite or lip position right.
Speaker 2 (05:57):
A lower lip that constantly rests behind the upper incisors
can maintain or worsen an overjet or even cause that
retroloclination you see in class to dift to and crowding.
We often think it's just big teeth, but the evidence
points more to arch size issues.
Speaker 1 (06:11):
And arch size is influenced by environment and function.
Speaker 2 (06:14):
Definitely less vigorous chewing in modern diets.
Speaker 1 (06:17):
Things like that.
Speaker 2 (06:18):
It's more about the mismatch between tooth size and available space,
and that space is influenced by function, not just genetics
dictating tooth size.
Speaker 1 (06:27):
Okay, this leads us nicely into craniofacial growth after birth.
It's not just simple enlargement. The source outlines four major
theories explaining how the face grows, involving relocation and displacement.
Speaker 2 (06:41):
Yeah, these theories kind of built on each other. First
was the sutral theory from Sitter and Winement. They thought
the sutures the joints between skull bones where the active
growth centers pushing things apart.
Speaker 1 (06:52):
That's not quite right, is it not?
Speaker 2 (06:53):
Really? We now see sutures as tension adapted. They respond
to bones being pulled apart by adding new bone, but
they don't generate the primary force themselves.
Speaker 1 (07:02):
So if not the sutures, then what That.
Speaker 2 (07:04):
Led James Scott to propose the cartilaginous theory. He argued
the real drivers were primary cartilages like the nasal septum
pushing the mid face down and forward, and the cartilage
and the cranial based sincondroses. The mandil's condyle was seen
as more of a secondary adaptive site.
Speaker 1 (07:20):
Then came Melvin Moss with a pretty radical idea the
functional matrix theory.
Speaker 2 (07:26):
Yeah, Moss flipped it. He said, bone is essentially passive.
Its growth is secondary to the function and the needs
of the surrounding soft tissues, the functional matrices.
Speaker 1 (07:34):
Can you break that down a bit microskeletal and macroskeletal units, sure.
Speaker 2 (07:38):
He said. The shape and size of a bone, like
where muscles attach, is determined by local perios steel matrices.
That's the microskeletal unit. But the position of the whole
bone in space, its displacement is driven by capsular matrices
like the growing brain pushing the skull bones out. That's
the macroskeletal unit. Function drives form and position.
Speaker 1 (07:59):
Fascinating, And the last one, the sero system theory tries
it tied all together.
Speaker 2 (08:03):
Kind of Yeah, Petrovic servo system is complex. It's a
cybernetic model. It suggests there's a genetically set comparator related
to the primary cartilages like the cranial base. The mandible
with its secondary cartilage growth at the condyle then serves
the system, adapting its growth based on feedback from the
occlusion and muscles to try and match that changing reference.
(08:23):
It integrates genetics and environment.
Speaker 1 (08:25):
Wow, Okay, that covers the biology of growth. Yeah, let's
get into biomechanics segment two. How do we actually move
teeth using forces? What are the principles?
Speaker 2 (08:36):
The absolute key concept you have to grasp is the
center of resistance core. Think of it as the balance
point of the tooth within the bone. If you could
push exactly on that point, the tooth would slide without tipping.
Speaker 1 (08:48):
And where is it?
Speaker 2 (08:49):
Roughly for a typical single rooted tooth, it's about a
third to halfway down the root length from the bone crust.
But here's the clinical kicker. If a patient loses bone
from gum disease, the core moves apically towards the root tip.
Speaker 1 (09:03):
Why does that matter so much?
Speaker 2 (09:04):
Because the force system you apply to the crown will
now have a different effect. A force that might have
caused bodily movement before could now cause massive, uncontrolled tipping
because the resistance point has shifted. Very important.
Speaker 1 (09:17):
So applying a simple force to the crown, which is
obviously not at the core, causes what kind of movement
it causes?
Speaker 2 (09:23):
Tipping? The crown moves one way, the root tip moves
the other. It's the easiest movement to achieve. Very typical
of simple removable appliances and.
Speaker 1 (09:31):
The harder movement bodily movement.
Speaker 2 (09:33):
Right bodily movement or translation where the crown and root
move together in the same direction. That's much harder. It
requires not just a force.
Speaker 1 (09:40):
But also a couple, A couple like two forces.
Speaker 2 (09:43):
Exactly, A couple is two equal and opposite forces acting
at a distance, creating a pure rotation or moment. To
get bodily movement, you need the main force plus a
counteracting moment from a couple to stop the tipping and
control the root.
Speaker 1 (09:57):
And that's where fixed appliances like braces with rectangular wires
come in.
Speaker 2 (10:01):
Precisely, the rectangular wire engaging the slot of the bracket
is specifically designed to deliver both the force and the
couple needed for that precise root control and bodily movement.
Speaker 1 (10:11):
Okay, so we apply force to move a tooth, but
Newton's third law says there's an equal and opposite reaction.
How do we manage that? Anchorage? Right?
Speaker 2 (10:20):
Exactly? Anchorage is all about resisting that unwonted reaction force.
You need something stable to push against. Traditionally we use
teeth with larger root surface area, or groups.
Speaker 1 (10:30):
Of teeth, or nowadays mini.
Speaker 2 (10:32):
Screws or nowadays absolute anchorage using things like mini screws
or temporary skeletal anchorage devices, they don't move at all,
providing rock solid anchorage. We also have to consider friction.
Speaker 1 (10:44):
Friction between the wire and the bracket.
Speaker 2 (10:46):
Yeah, it resists the sliding movement we often need. Static
friction has to be overcome to start movement, and kinetic
friction resists it once it's going.
Speaker 1 (10:55):
And what affects how much friction there is? Materials?
Speaker 2 (10:59):
Materials matter a lot. Stainless steel archwires generally have lower
friction than say, beta titanium, and ceramic brackets tend to
have higher friction than metal ones. The angle the wire
makes with the bracket slot also plays a big role.
More friction means wasted force and slower treatment.
Speaker 1 (11:16):
Good to know, all right, let's switch to diagnosis before
we even look at teeth. What systemic health issues do
We absolutely need to screen.
Speaker 2 (11:22):
For medical history and first always you need to know
about things like uncontrolled diabetes or conditions requiring immunosuppressants because
they mess with bone healing. Allergies are crucial too, especially nickel,
which is in most standard archwires.
Speaker 3 (11:35):
And latex then the exteral exam looking at the face
YEP assess natural head posture, facial symmetry, proportions those facial thirds,
and crucially smile aesthetics.
Speaker 1 (11:46):
How much tooth and gum shows? How does the smile
line relate to the lips? This sense your esthetic goals?
Speaker 2 (11:52):
Okay? Then radiographs. Standard views are the panoramic, the DPT,
and the lateral seph right, but with fixed braces comes
a big risk.
Speaker 1 (12:01):
The biggest clinical headache, honestly is enamel decalcification. Those white
spot lesions. The source site's incidence as high as fifty
percent in fixed appliance patients. Fifty percent. That's huge, It's massive.
It means pristine oral hygiene is non negotiable, and regular
use of topical fluoride like a point zero five percent
sodium chloride mouthwashed daily is pretty much standard protocol to
(12:23):
help prevent it.
Speaker 2 (12:24):
What about the other biological riskot resorption.
Speaker 1 (12:27):
Yeah, some microscopic route shortening happens to almost everyone during ORTHO,
but severe resorption losing like a quarter of the root
or more, that's rare, maybe less than three percent of patients.
Speaker 2 (12:36):
What are the biggest risk factors for that severe resorption.
The evidence points strongly to two main things, the total
duration of active treatment and the distance the teeth have
to move. Longer treatment, bigger movements higher risk. Also, heavy
intrusive forces are particularly risky.
Speaker 1 (12:53):
Let's talk cephalometrics. The A and B angle is used
all the time to assess the skeletal jaw relationship. But
you mentioned it has a flaw.
Speaker 2 (13:01):
It does A and B measures the angle between nation
and point A maxilla and point B mandible. The problem
is it's super sensitive to where nation sits vertically. If
nation is unusually high or low on the face, it
can completely throw off the amb reading, making a skeletal
pattern look better or worse than it actually is.
Speaker 1 (13:20):
So how we correct for that Mills Eastman correction exactly.
Speaker 2 (13:23):
Mills's correction is a way to adjust the A and
B angle based on the SNA angle, which relates the
maxilla to the cranial base. If SNA is high, suggesting
nation might be forward, you subtract a bit from A
and B. If SNA is low, you add a bit.
It tries to normalize the reading.
Speaker 1 (13:38):
Okay, now here's a really interesting point from the source
that challenges some old ortho rules, the idea of positioning
the lower incisor edge on or slightly ahead of the
Apagonian line for stability. What's the verdict?
Speaker 2 (13:50):
This is huge? The source basically says there's no solid
evidence to back that up decades of aiming for that
specific one millimeter ahead of a pogline. The research doesn't
confirm it guarantees stability or better aesthetics.
Speaker 1 (14:03):
Wow, so focusing purely on that two D measurement might
be missing the bigger picture.
Speaker 2 (14:07):
It seems so soft tissue balance and limits are likely
far more important for long term stability than hitting an
arbitrary cephalmetric line. It's a major clinical.
Speaker 1 (14:16):
Takeaway, definitely food for thought. Quickly, what about IOTN and.
Speaker 2 (14:20):
TMD IOTN the index of treatment need is vital, particularly
in places with public health care, for prioritizing who gets
treatment based on dental health needs and aesthetics. As for
TMD temporal mandibular disorders, the source is quite clear there's
a lack of robust evidence linking orthodonic treatment itself, even
with extractions to causing TMD.
Speaker 1 (14:40):
So treatment is generally considered neutral regarding TMD risk pretty much.
Speaker 2 (14:45):
But you absolutely need a good baseline assessment of jaw
joint health before you start any treatment.
Speaker 1 (14:51):
Okay, final stretch Segment three Treatment planning timing matters, especially
for using growth. When's the best window for mo standard orthocases?
Speaker 2 (15:01):
Generally the sweet spot is the late mixed dentician just
before those last baby molars the ease fall out. You
catch the peak adolescent growth spurt, which can help correct
jaw discregancies, and it often leads to the shortest overall
treatment time.
Speaker 1 (15:15):
Are there exceptions cases where you treat earlier.
Speaker 2 (15:18):
The main one is severe class three where the upper
job is underdeveloped maxillary hypopleasia. Starting interceptive treatment early, maybe
in the early mixed dentition with something like a protraction
headgear or face mask, can give you a much better
skeletal response.
Speaker 1 (15:34):
And treatment planning itself is shifted, hasn't it. We don't
just look at the teeth and isolation anymore, not at all.
Speaker 2 (15:39):
The modern approach, influenced by people like Ackerman and Profit,
is all about soft tissue limits. You start with the face.
Where should the incisors be for optimal lip support and
smile aesthetics. That dictates everything else.
Speaker 1 (15:50):
So the facial goals determine whether you extract camouflage modify growth.
Speaker 2 (15:54):
Precisely, it's an outside end approach. Especially for the upper incisors.
Their position relative to the lips is paramount.
Speaker 1 (16:02):
Okay, talking about managing discrepancies, let's focus on Class two,
the lower job being back. If we're using growth modification
with functional appliances, what's the key principle regarding the lower incisors.
Speaker 2 (16:13):
The golden rule generally is avoid proclining the lower incisors.
Pushing them forward off the bone is notoriously unstable and
prone to relapse. The only real exception is if they
start severely tipped back, like in a class two divto Otherwise,
you want the correction to come from skeletal change or
upper tooth movement, not by flaring the lower front.
Speaker 1 (16:33):
Teeth, and functional appliances like the twin block help achieve
that skeletal change.
Speaker 2 (16:38):
Yes, appliances like the twin block are designed to posture
the mandible forward during growth, encouraging more favorable growth expression.
Speaker 1 (16:45):
Tell us a bit more about the twin block specifically,
what makes it work.
Speaker 2 (16:49):
The twin block, developed by Clark back in eighty eight,
is clever. It's two separate removable plates upper and lower.
With these angled plastic blocks usually inclined about seventy degrees.
Speaker 1 (17:01):
And the angle forces the jaw forward exactly.
Speaker 2 (17:04):
To bite together comfortably, the patient has to posture forward.
The blocks usually need about five millimeters of vertical opening
between them to engage properly. It's popular because it works
fast for overjet reduction and kids tend to wear them
reasonably well.
Speaker 1 (17:18):
Any common side effects.
Speaker 2 (17:20):
The most common one is a temporary lateral open bite
because the blocks keep the back teeth apart. Sometimes they
don't erupt fully together initially, but that's usually easy to
fix by trimming the block strategically towards the end of
the functional phase.
Speaker 1 (17:32):
Right now, the hard truth relapse things wanting to move back.
What tends to be most unstable after treatment.
Speaker 2 (17:40):
Relapse is almost a given to some degree, especially lower
incisor crowding tends to creep back over time. The source
highlights a few things particularly prone to relapse. Rotated teeth,
those periodontal fibers have long memories closing spaces, and especially
any expansion of the lower intercnine with trying to wide
the arch between the lower canines is very unstable long.
Speaker 1 (18:03):
Term, which is why retention is so critical, absolutely essential.
Speaker 2 (18:07):
Often requires long term, even permanent retention, especially fixed retainers
bonded to the back of the lower front teeth, usually
a multi strand stainless steel wire. That's often the best
bet for holding corrections involving those unstable lower incisors or
significant expansion.
Speaker 1 (18:23):
This has been incredibly comprehensive. We've gone from the cellular
level of bone remodeling, through biomechanics, grow theories, diagnosis all
the way to appliance choices and retention strategies. It really
covers the foundational knowledge from those early chapters.
Speaker 2 (18:36):
It does, and the key for anyone listening students new
dentist is to connect these dots. Understand why the center
of resistance matters when you apply force, know the risks
like root resorption and decalcification, use the diagnostic tools like
cefs wisely, but always plan based on the face and
soft tissues. First.
Speaker 1 (18:55):
Okay, let's wrap up with a review question, a scenario
for you to think about based on what we've discussed.
If a patient comes in with a severe class two
division two malaclusion. Remember that's class two molars, but retroclined
upper incisors a deep bite in your planning treatment with
fixed braces. Yeah, what's the main biomechanical challenge in correcting
those upper incisors.
Speaker 2 (19:16):
And importantly, why might correcting this specific type of incisor
relationship actually have pretty good long term stability compared to say,
just trying to procline an average lower incisor.
Speaker 1 (19:27):
Think about the movement needed and the surrounding tissues.
Speaker 2 (19:30):
The main challenge is getting controlled proclination and intrusion of
those upper incisors. You need to tip them forward and
lift them up to level the byte plane and get
a good inter incisal angle. The reason it can be
stable is that you're often moving them into a more
functionally favorable position, supported better by the lower lip, rather
than fighting against the existing soft tissue pressures. You're using
(19:53):
the initial retroclination to your advantage in a way.
Speaker 1 (19:56):
That's a great way to put it a perfect clinical
tie in. So here's our final thought for you to
mull over. We've talked about the science, the mechanics, the diagnostics,
but even with perfect planning, the biggest variable often comes
down to the patient right compliance. How are you going
to measure encourage and sustain that crucial human factor in
your own practice, something.
Speaker 2 (20:18):
To consider, Definitely something to think about.
Speaker 1 (20:20):
Thanks for joining us for this deep tive. We'll catch
you next time.
Welcome back to the deep dive. Today. We're really getting
into some foundational knowledge for anyone heading into dentistry, especially orthodonics.
That's right. Our source is a classic, The Handbook of
Orthogotics by Dibious from two thousand and nine.
Speaker 2 (00:14):
A cornerstone text.
Speaker 1 (00:15):
Yeah, and if you're a student or maybe just starting out,
you know these early chapters are packed angles, classifications, growth theories.
It's a lot, it is.
Speaker 2 (00:26):
So our goal today is to kind of cut through that,
synthesize the really key concepts classification, development, diagnosis, the basic
principles you need exactly.
Speaker 1 (00:37):
We want to give you a complete, detailed summary, but
you know, make it stick, provide those core scientific nuggets
you need for clinical practice.
Speaker 2 (00:43):
And we have to start some more fundamental like what
even is normal occlusion?
Speaker 1 (00:47):
Good starting point, so when we talk aclusion, there's static
and functional. Right. Historically, where did the idea of ideal
static occlusion come from?
Speaker 2 (00:56):
Well you have to start with Edward Engel. His whole
focus really was on the first permanent.
Speaker 1 (01:00):
Molars, just the molars pretty much.
Speaker 2 (01:03):
He defined normal occlusion based on one thing, the mesiobuckle
cusp of the upper first molar, fitting neatly into the
sulcus between the buckle cusps of the lower first molar.
That was his key to the whole system.
Speaker 1 (01:15):
Okay, but we know now that just having the molars
line up isn't the whole picture for a great smile
or a stable bike. H What did Laurence Andrews ad
later with his six keys?
Speaker 2 (01:26):
Right, Andrews really fleshed it out. He gave us a
much more detailed blueprint for what an ideal finish looks like.
His six keys covered the molar relationship, sure, like angles,
but also things like specific crown angulation the tip you know,
messiodistally and crown inclination which is the torque labiolingually plus
no rotations, tight contacts, the works.
Speaker 1 (01:47):
And these keys are still fundamental today for treatment goals
right for aesthetics.
Speaker 2 (01:50):
And still absolutely they define what we're aiming for.
Speaker 1 (01:53):
Okay, so that's static. What about when the jaw is
actually moving functional occlusion? What needs to happen then too?
Speaker 2 (01:59):
Like protective teeth, functionally it's about guidance and contacts. You
need what's called anterior protection. So when you move your
jaw side to side, ideally, only the canines should be
touching and guiding the movement. That's canine guidance or sometimes
group function or sometimes yeah, a few posterior teeth might
share the load, that's group function. But the main goal
(02:20):
is immediate separation disclusion of all the other back teeth.
Same idea, when you move forward protrusion, only the incisors
should guide incisile guidance.
Speaker 1 (02:29):
And why is that separation that disclusion so important?
Speaker 2 (02:32):
It minimizes harmful sideways or sheer forces on the molars
and premolars. They are designed for that. So that's the
first thing. Second is posterior protection, meaning meaning when you
bite down fully in your maximum bite what we call
ICP intercustible position, you need solid simultaneous contacts on both
sides in the back, multiple posterior teeth hitting evenly.
Speaker 1 (02:54):
Okay, And what about the front teeth in that.
Speaker 2 (02:56):
Position, Critically, the front teeth the incisors should ideally be
just slightly out of contact and ICP no heavy anterior
contact stopping you from fully closing in the back.
Speaker 1 (03:06):
Makes sense? And the third piece you often hear COO
and CR mentioned ICP and RCP. Now I guess right.
Speaker 2 (03:13):
The third point is a relationship between that maximum byte ICP,
which used to be called centric occlusion or CO, and
the jaw's most retruded hinge position RCP or retruded contact position,
sometimes called cr and Ideally, ideally these two positions should
be very close together, maybe just a tiny bit of
freedom to slide forward from RCP into ICP. If there's
(03:35):
a big difference, a big slide, it often points to
an interference or instability.
Speaker 1 (03:39):
Okay, so that defines our baseline normal. Now let's talk
about when thing's deviate malaclusion. If the molars aren't class one,
we use angles system.
Speaker 2 (03:47):
Right yeap Angle's classification is still the workhorse. Class one
is that ideal molar relationship we talked about. Class two
means the lower molar is distal, or further back than
it should.
Speaker 1 (03:56):
Be, and that's split into division one and two. Correct.
Speaker 2 (03:59):
Division one is class two molars with flared out protruding
upper incisors. Division two is class two molars but with
the upper incisors tipped.
Speaker 1 (04:07):
Back retroclined, and class three.
Speaker 2 (04:09):
Class three is the opposite. The lower molar is mesial
or further forward than normal. And remember clinically, it's rarely
a perfect full cusp difference. We often describe these relationships
more precisely, like half unit class two or third unit
class three.
Speaker 1 (04:26):
Got it, And then there's a parallel system just for
the incisors the British standards one exactly.
Speaker 2 (04:31):
The incisor classification looks purely at the front teeth, specifically
where the lower incisor edge sits relative to the singularm plateau,
that little bump on the back of the upper incisors.
Speaker 1 (04:41):
The class one is normal.
Speaker 2 (04:42):
Class one is normal, the lower incisor hits the singular area.
Class two it's behind the singulum again. Div one if
the upper incisors are proclined, If two if they're.
Speaker 1 (04:50):
Retroclined, and class three incisors.
Speaker 2 (04:52):
That's when the lower incisor edge is in front of
the upper singulum plateau. So you have a reduced or
even reverse overjet and underbyte essentially.
Speaker 1 (05:00):
Okay, that covers classification. Let's shift gears to why maleeclusions
happen Etiology, the classic nature versus nurture debate. What does
the source say about strong genetic links?
Speaker 2 (05:11):
Oh, genetics is definitely a major player for some things.
The source highlights skeletal patterns, especially mendibular prognathism. You know
of strong lower jaw class three that shows really high
heritbility runs in families.
Speaker 1 (05:24):
Any other examples.
Speaker 2 (05:26):
Yes, Specific dental anomalies too, like pallatally impacted canines, those
upper canines stuck in the roof of the mouth. They're
often linked genetically with missing or small lateral incisors in
the same family. It's a pattern, but it's.
Speaker 1 (05:38):
Not all genes. Right. The environment must play a role.
Where does that come in?
Speaker 2 (05:42):
Absolutely, the environment, often acting through the soft tissue envelope,
is huge. Think about habits. A persistent thumb or finger
sucking habit that can push the upper incisors forward, create an.
Speaker 1 (05:55):
Open bite or lip position right.
Speaker 2 (05:57):
A lower lip that constantly rests behind the upper incisors
can maintain or worsen an overjet or even cause that
retroloclination you see in class to dift to and crowding.
We often think it's just big teeth, but the evidence
points more to arch size issues.
Speaker 1 (06:11):
And arch size is influenced by environment and function.
Speaker 2 (06:14):
Definitely less vigorous chewing in modern diets.
Speaker 1 (06:17):
Things like that.
Speaker 2 (06:18):
It's more about the mismatch between tooth size and available space,
and that space is influenced by function, not just genetics
dictating tooth size.
Speaker 1 (06:27):
Okay, this leads us nicely into craniofacial growth after birth.
It's not just simple enlargement. The source outlines four major
theories explaining how the face grows, involving relocation and displacement.
Speaker 2 (06:41):
Yeah, these theories kind of built on each other. First
was the sutral theory from Sitter and Winement. They thought
the sutures the joints between skull bones where the active
growth centers pushing things apart.
Speaker 1 (06:52):
That's not quite right, is it not?
Speaker 2 (06:53):
Really? We now see sutures as tension adapted. They respond
to bones being pulled apart by adding new bone, but
they don't generate the primary force themselves.
Speaker 1 (07:02):
So if not the sutures, then what That.
Speaker 2 (07:04):
Led James Scott to propose the cartilaginous theory. He argued
the real drivers were primary cartilages like the nasal septum
pushing the mid face down and forward, and the cartilage
and the cranial based sincondroses. The mandil's condyle was seen
as more of a secondary adaptive site.
Speaker 1 (07:20):
Then came Melvin Moss with a pretty radical idea the
functional matrix theory.
Speaker 2 (07:26):
Yeah, Moss flipped it. He said, bone is essentially passive.
Its growth is secondary to the function and the needs
of the surrounding soft tissues, the functional matrices.
Speaker 1 (07:34):
Can you break that down a bit microskeletal and macroskeletal units, sure.
Speaker 2 (07:38):
He said. The shape and size of a bone, like
where muscles attach, is determined by local perios steel matrices.
That's the microskeletal unit. But the position of the whole
bone in space, its displacement is driven by capsular matrices
like the growing brain pushing the skull bones out. That's
the macroskeletal unit. Function drives form and position.
Speaker 1 (07:59):
Fascinating, And the last one, the sero system theory tries
it tied all together.
Speaker 2 (08:03):
Kind of Yeah, Petrovic servo system is complex. It's a
cybernetic model. It suggests there's a genetically set comparator related
to the primary cartilages like the cranial base. The mandible
with its secondary cartilage growth at the condyle then serves
the system, adapting its growth based on feedback from the
occlusion and muscles to try and match that changing reference.
(08:23):
It integrates genetics and environment.
Speaker 1 (08:25):
Wow, Okay, that covers the biology of growth. Yeah, let's
get into biomechanics segment two. How do we actually move
teeth using forces? What are the principles?
Speaker 2 (08:36):
The absolute key concept you have to grasp is the
center of resistance core. Think of it as the balance
point of the tooth within the bone. If you could
push exactly on that point, the tooth would slide without tipping.
Speaker 1 (08:48):
And where is it?
Speaker 2 (08:49):
Roughly for a typical single rooted tooth, it's about a
third to halfway down the root length from the bone crust.
But here's the clinical kicker. If a patient loses bone
from gum disease, the core moves apically towards the root tip.
Speaker 1 (09:03):
Why does that matter so much?
Speaker 2 (09:04):
Because the force system you apply to the crown will
now have a different effect. A force that might have
caused bodily movement before could now cause massive, uncontrolled tipping
because the resistance point has shifted. Very important.
Speaker 1 (09:17):
So applying a simple force to the crown, which is
obviously not at the core, causes what kind of movement
it causes?
Speaker 2 (09:23):
Tipping? The crown moves one way, the root tip moves
the other. It's the easiest movement to achieve. Very typical
of simple removable appliances and.
Speaker 1 (09:31):
The harder movement bodily movement.
Speaker 2 (09:33):
Right bodily movement or translation where the crown and root
move together in the same direction. That's much harder. It
requires not just a force.
Speaker 1 (09:40):
But also a couple, A couple like two forces.
Speaker 2 (09:43):
Exactly, A couple is two equal and opposite forces acting
at a distance, creating a pure rotation or moment. To
get bodily movement, you need the main force plus a
counteracting moment from a couple to stop the tipping and
control the root.
Speaker 1 (09:57):
And that's where fixed appliances like braces with rectangular wires
come in.
Speaker 2 (10:01):
Precisely, the rectangular wire engaging the slot of the bracket
is specifically designed to deliver both the force and the
couple needed for that precise root control and bodily movement.
Speaker 1 (10:11):
Okay, so we apply force to move a tooth, but
Newton's third law says there's an equal and opposite reaction.
How do we manage that? Anchorage? Right?
Speaker 2 (10:20):
Exactly? Anchorage is all about resisting that unwonted reaction force.
You need something stable to push against. Traditionally we use
teeth with larger root surface area, or groups.
Speaker 1 (10:30):
Of teeth, or nowadays mini.
Speaker 2 (10:32):
Screws or nowadays absolute anchorage using things like mini screws
or temporary skeletal anchorage devices, they don't move at all,
providing rock solid anchorage. We also have to consider friction.
Speaker 1 (10:44):
Friction between the wire and the bracket.
Speaker 2 (10:46):
Yeah, it resists the sliding movement we often need. Static
friction has to be overcome to start movement, and kinetic
friction resists it once it's going.
Speaker 1 (10:55):
And what affects how much friction there is? Materials?
Speaker 2 (10:59):
Materials matter a lot. Stainless steel archwires generally have lower
friction than say, beta titanium, and ceramic brackets tend to
have higher friction than metal ones. The angle the wire
makes with the bracket slot also plays a big role.
More friction means wasted force and slower treatment.
Speaker 1 (11:16):
Good to know, all right, let's switch to diagnosis before
we even look at teeth. What systemic health issues do
We absolutely need to screen.
Speaker 2 (11:22):
For medical history and first always you need to know
about things like uncontrolled diabetes or conditions requiring immunosuppressants because
they mess with bone healing. Allergies are crucial too, especially nickel,
which is in most standard archwires.
Speaker 3 (11:35):
And latex then the exteral exam looking at the face
YEP assess natural head posture, facial symmetry, proportions those facial thirds,
and crucially smile aesthetics.
Speaker 1 (11:46):
How much tooth and gum shows? How does the smile
line relate to the lips? This sense your esthetic goals?
Speaker 2 (11:52):
Okay? Then radiographs. Standard views are the panoramic, the DPT,
and the lateral seph right, but with fixed braces comes
a big risk.
Speaker 1 (12:01):
The biggest clinical headache, honestly is enamel decalcification. Those white
spot lesions. The source site's incidence as high as fifty
percent in fixed appliance patients. Fifty percent. That's huge, It's massive.
It means pristine oral hygiene is non negotiable, and regular
use of topical fluoride like a point zero five percent
sodium chloride mouthwashed daily is pretty much standard protocol to
(12:23):
help prevent it.
Speaker 2 (12:24):
What about the other biological riskot resorption.
Speaker 1 (12:27):
Yeah, some microscopic route shortening happens to almost everyone during ORTHO,
but severe resorption losing like a quarter of the root
or more, that's rare, maybe less than three percent of patients.
Speaker 2 (12:36):
What are the biggest risk factors for that severe resorption.
The evidence points strongly to two main things, the total
duration of active treatment and the distance the teeth have
to move. Longer treatment, bigger movements higher risk. Also, heavy
intrusive forces are particularly risky.
Speaker 1 (12:53):
Let's talk cephalometrics. The A and B angle is used
all the time to assess the skeletal jaw relationship. But
you mentioned it has a flaw.
Speaker 2 (13:01):
It does A and B measures the angle between nation
and point A maxilla and point B mandible. The problem
is it's super sensitive to where nation sits vertically. If
nation is unusually high or low on the face, it
can completely throw off the amb reading, making a skeletal
pattern look better or worse than it actually is.
Speaker 1 (13:20):
So how we correct for that Mills Eastman correction exactly.
Speaker 2 (13:23):
Mills's correction is a way to adjust the A and
B angle based on the SNA angle, which relates the
maxilla to the cranial base. If SNA is high, suggesting
nation might be forward, you subtract a bit from A
and B. If SNA is low, you add a bit.
It tries to normalize the reading.
Speaker 1 (13:38):
Okay, now here's a really interesting point from the source
that challenges some old ortho rules, the idea of positioning
the lower incisor edge on or slightly ahead of the
Apagonian line for stability. What's the verdict?
Speaker 2 (13:50):
This is huge? The source basically says there's no solid
evidence to back that up decades of aiming for that
specific one millimeter ahead of a pogline. The research doesn't
confirm it guarantees stability or better aesthetics.
Speaker 1 (14:03):
Wow, so focusing purely on that two D measurement might
be missing the bigger picture.
Speaker 2 (14:07):
It seems so soft tissue balance and limits are likely
far more important for long term stability than hitting an
arbitrary cephalmetric line. It's a major clinical.
Speaker 1 (14:16):
Takeaway, definitely food for thought. Quickly, what about IOTN and.
Speaker 2 (14:20):
TMD IOTN the index of treatment need is vital, particularly
in places with public health care, for prioritizing who gets
treatment based on dental health needs and aesthetics. As for
TMD temporal mandibular disorders, the source is quite clear there's
a lack of robust evidence linking orthodonic treatment itself, even
with extractions to causing TMD.
Speaker 1 (14:40):
So treatment is generally considered neutral regarding TMD risk pretty much.
Speaker 2 (14:45):
But you absolutely need a good baseline assessment of jaw
joint health before you start any treatment.
Speaker 1 (14:51):
Okay, final stretch Segment three Treatment planning timing matters, especially
for using growth. When's the best window for mo standard orthocases?
Speaker 2 (15:01):
Generally the sweet spot is the late mixed dentician just
before those last baby molars the ease fall out. You
catch the peak adolescent growth spurt, which can help correct
jaw discregancies, and it often leads to the shortest overall
treatment time.
Speaker 1 (15:15):
Are there exceptions cases where you treat earlier.
Speaker 2 (15:18):
The main one is severe class three where the upper
job is underdeveloped maxillary hypopleasia. Starting interceptive treatment early, maybe
in the early mixed dentition with something like a protraction
headgear or face mask, can give you a much better
skeletal response.
Speaker 1 (15:34):
And treatment planning itself is shifted, hasn't it. We don't
just look at the teeth and isolation anymore, not at all.
Speaker 2 (15:39):
The modern approach, influenced by people like Ackerman and Profit,
is all about soft tissue limits. You start with the face.
Where should the incisors be for optimal lip support and
smile aesthetics. That dictates everything else.
Speaker 1 (15:50):
So the facial goals determine whether you extract camouflage modify growth.
Speaker 2 (15:54):
Precisely, it's an outside end approach. Especially for the upper incisors.
Their position relative to the lips is paramount.
Speaker 1 (16:02):
Okay, talking about managing discrepancies, let's focus on Class two,
the lower job being back. If we're using growth modification
with functional appliances, what's the key principle regarding the lower incisors.
Speaker 2 (16:13):
The golden rule generally is avoid proclining the lower incisors.
Pushing them forward off the bone is notoriously unstable and
prone to relapse. The only real exception is if they
start severely tipped back, like in a class two divto Otherwise,
you want the correction to come from skeletal change or
upper tooth movement, not by flaring the lower front.
Speaker 1 (16:33):
Teeth, and functional appliances like the twin block help achieve
that skeletal change.
Speaker 2 (16:38):
Yes, appliances like the twin block are designed to posture
the mandible forward during growth, encouraging more favorable growth expression.
Speaker 1 (16:45):
Tell us a bit more about the twin block specifically,
what makes it work.
Speaker 2 (16:49):
The twin block, developed by Clark back in eighty eight,
is clever. It's two separate removable plates upper and lower.
With these angled plastic blocks usually inclined about seventy degrees.
Speaker 1 (17:01):
And the angle forces the jaw forward exactly.
Speaker 2 (17:04):
To bite together comfortably, the patient has to posture forward.
The blocks usually need about five millimeters of vertical opening
between them to engage properly. It's popular because it works
fast for overjet reduction and kids tend to wear them
reasonably well.
Speaker 1 (17:18):
Any common side effects.
Speaker 2 (17:20):
The most common one is a temporary lateral open bite
because the blocks keep the back teeth apart. Sometimes they
don't erupt fully together initially, but that's usually easy to
fix by trimming the block strategically towards the end of
the functional phase.
Speaker 1 (17:32):
Right now, the hard truth relapse things wanting to move back.
What tends to be most unstable after treatment.
Speaker 2 (17:40):
Relapse is almost a given to some degree, especially lower
incisor crowding tends to creep back over time. The source
highlights a few things particularly prone to relapse. Rotated teeth,
those periodontal fibers have long memories closing spaces, and especially
any expansion of the lower intercnine with trying to wide
the arch between the lower canines is very unstable long.
Speaker 1 (18:03):
Term, which is why retention is so critical, absolutely essential.
Speaker 2 (18:07):
Often requires long term, even permanent retention, especially fixed retainers
bonded to the back of the lower front teeth, usually
a multi strand stainless steel wire. That's often the best
bet for holding corrections involving those unstable lower incisors or
significant expansion.
Speaker 1 (18:23):
This has been incredibly comprehensive. We've gone from the cellular
level of bone remodeling, through biomechanics, grow theories, diagnosis all
the way to appliance choices and retention strategies. It really
covers the foundational knowledge from those early chapters.
Speaker 2 (18:36):
It does, and the key for anyone listening students new
dentist is to connect these dots. Understand why the center
of resistance matters when you apply force, know the risks
like root resorption and decalcification, use the diagnostic tools like
cefs wisely, but always plan based on the face and
soft tissues. First.
Speaker 1 (18:55):
Okay, let's wrap up with a review question, a scenario
for you to think about based on what we've discussed.
If a patient comes in with a severe class two
division two malaclusion. Remember that's class two molars, but retroclined
upper incisors a deep bite in your planning treatment with
fixed braces. Yeah, what's the main biomechanical challenge in correcting
those upper incisors.
Speaker 2 (19:16):
And importantly, why might correcting this specific type of incisor
relationship actually have pretty good long term stability compared to say,
just trying to procline an average lower incisor.
Speaker 1 (19:27):
Think about the movement needed and the surrounding tissues.
Speaker 2 (19:30):
The main challenge is getting controlled proclination and intrusion of
those upper incisors. You need to tip them forward and
lift them up to level the byte plane and get
a good inter incisal angle. The reason it can be
stable is that you're often moving them into a more
functionally favorable position, supported better by the lower lip, rather
than fighting against the existing soft tissue pressures. You're using
(19:53):
the initial retroclination to your advantage in a way.
Speaker 1 (19:56):
That's a great way to put it a perfect clinical
tie in. So here's our final thought for you to
mull over. We've talked about the science, the mechanics, the diagnostics,
but even with perfect planning, the biggest variable often comes
down to the patient right compliance. How are you going
to measure encourage and sustain that crucial human factor in
your own practice, something.
Speaker 2 (20:18):
To consider, Definitely something to think about.
Speaker 1 (20:20):
Thanks for joining us for this deep tive. We'll catch
you next time.
Popular Podcasts
CrimeLess: Hillbilly Heist
It’s 1996 in rural North Carolina, and an oddball crew makes history when they pull off America’s third largest cash heist. But it’s all downhill from there. Join host Johnny Knoxville as he unspools a wild and woolly tale about a group of regular ‘ol folks who risked it all for a chance at a better life. CrimeLess: Hillbilly Heist answers the question: what would you do with 17.3 million dollars? The answer includes diamond rings, mansions, velvet Elvis paintings, plus a run for the border, murder-for-hire-plots, and FBI busts.
Crime Junkie
Does hearing about a true crime case always leave you scouring the internet for the truth behind the story? Dive into your next mystery with Crime Junkie. Every Monday, join your host Ashley Flowers as she unravels all the details of infamous and underreported true crime cases with her best friend Brit Prawat. From cold cases to missing persons and heroes in our community who seek justice, Crime Junkie is your destination for theories and stories you won’t hear anywhere else. Whether you're a seasoned true crime enthusiast or new to the genre, you'll find yourself on the edge of your seat awaiting a new episode every Monday. If you can never get enough true crime... Congratulations, you’ve found your people. Follow to join a community of Crime Junkies! Crime Junkie is presented by audiochuck Media Company.
Stuff You Should Know
If you've ever wanted to know about champagne, satanism, the Stonewall Uprising, chaos theory, LSD, El Nino, true crime and Rosa Parks, then look no further. Josh and Chuck have you covered.